Dependency Management

In Polypheny, we manage our Java dependencies via Gradle, aiming for consistency and maintainability across our stack. This guideline outlines the best practices for integrating these dependencies into Polypheny-DB and other components of the Polypheny stack.

‘java-library’ Plugin

In Polypheny-DB, we use the java-library plugin instead of the java plugin. The java-library plugin offers extended capabilities over the java plugin, allowing a more refined handling of dependencies. For more information on the java-library plugin, you can refer to the official documentation.

Adding Dependencies

The java-library plugin introduces two new configurations, api and implementation, that we use in place of compile for adding dependencies.


The api configuration should be used when you want to include a dependency that needs to be available to all other subprojects having your project as a dependency. Here is an example:

dependencies {
    api group: "com.example", name: "example-lib", version: example_lib_version


The implementation configuration should be used when a dependency is required merely for the implementation of your functionality and doesn’t need to be exposed to the subprojects that include your project. Here is an example:

dependencies {
    implementation group: "com.example", name: "example-lib", version: example_lib_version
If you are unsure, you probably want to use implementation.

Test Dependencies

Test dependencies are those libraries that are used solely for testing purposes and are not required in production runtime. Just like our regular dependencies, we manage these using Gradle.

Just like the main dependencies, test dependencies are added using the testImplementation and testApi configurations. The distinction between these two is the same as for implementation and api configurations, but it’s applied to the testing context. That is, testImplementation is used when a dependency is needed only for testing within the module, and testApi is used when a testing dependency needs to be shared among multiple modules.

In order to make the test classes of the core module available, you can add them as dependency:

testImplementation project(path: ":core", configuration: "tests")

Version Numbers

To ensure that all subprojects use the same version of a dependency, we store version numbers in the file. This approach fosters consistency across our projects.

In your build.gradle file, the version part should reference the property from For instance:

dependencies {
    implementation group: "com.example", name: "example-lib", version: example_lib_version

Then, you need to add a corresponding entry in the file like so:

example_lib_version = 23.1.2

Gradle Licensee Plugin

The Gradle Licensee plugin is a nifty tool we used to check the licenses of our project dependencies. It works by scanning the project’s dependencies and comparing them against a list of allowable licenses. This ensures that only dependencies with licenses that comply with your project’s licensing policy are bening used.

The plugin is configured to fail the build if it encounters any dependency with an unacceptable or unknown license. It is automatically applied to all modules in Polypheny-DB.

licensee {
    allowDependency('com.example', 'example-lib', '1.15') { because 'Reason why it compatible (e.g., the license)' }

The allowDependency function is used to explicitly allow specific dependencies that might not be covered by the licenses stated in the allow functions. This is particularly useful when a dependency’s licensing is compatible with Polypheny’s licensing policy, but may not be automatically recognized by the plugin. Remember to include a justification for allowing the dependency, providing transparency and maintainability to your codebase.

Importantly, as a safety measure, when adding dependencies in this manner, do not use the version variable defined in the file. Instead, explicitly state the version in the allowDependency function. This provides an additional layer of protection, ensuring that the dependency is validated for the exact version specified.

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